NASA's Opportunity Mars rover has gone into minimal operating mode as it rides out a giant dust storm that is blotting out the Sun. The storm, which is much worse than originally thought, is preventing the solar panels from recharging the veteran probe's batteries, but mission control have said that NASA engineers received a signal from Opportunity on Sunday morning.

One of Mars' more unusual characteristics is its tendency to generate dust storms of incredible size. When NASA's Mariner 9 orbiter arrived at Mars in 1971, there was a storm so great that it engulfed the entire planet and left the surface blotted out for two months. This fact is not only of scientific interest, it also has an impact of present and future missions to the Red Planet.

Unlike the nuclear-powered Curiosity rover, Opportunity relies on solar panels to keep its batteries charged. If those panels don't receive enough sunlight, the batteries will drain and the rover will be unable to power its heating units. Since the nights on Mars can get as cold as −225° F (−143° C), Opportunity's systems would freeze and never be able to restart again, as likely happened to its sister Spirit rover in 2010.

According to NASA, the present storm was detected by the space agency's Mars Reconnaissance Orbiter (MRO) on June 1. It now covers an area of 7 million mi² (18 million km²) or about that of North America, including Opportunity's location in Perseverance Valley. The concern of mission control is that the light levels from the airborne dust might increase the opacity level to the point where the panels would not get enough light, so the rover was ordered to suspend all science operations and concentrate battery power on running the heaters and telemetry.

However, the storm turned out to be more severe than predicted. Where a similar storm encountered by Opportunity in 2007 had an opacity or tau of 5.5, the present one is pegging at 10.8 tau. Despite this, mission control was able to use NASA's Deep Space Network (DSN) to establish contact on Sunday morning, proving that the spacecraft is still operating.

One benefit of the dust storm, however, is its role as an insulator that traps the atmosphere's heat, therefore limiting the extreme temperature swings on the Mars surface. Onboard instruments showed the rover's temperature to be –20° F (–29° C) at the latest data transmission, reducing the drain on the batteries while the systems generate heat of their own to help keep the rover warm.

Opportunity was launched on July 7, 2003 atop a Delta II rocket from Cape Canaveral Air Force Station, Florida. The Boeing-built, 408-lb (185-kg) rover, also known as Mars Exploration Rover-B (MER-A), landed on the Meridiani Planum region of Mars on January 25, 2004 – three weeks after its sister rover, Spirit (MER-A). Though Opportunity was designed to only operate for 90 days, it has continued to explore the planet for over 15 years.

Source: NASA

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